What is different about Lion?
It is the most significant change since probably Tiger.
What is the same about Lion?
Just like every other step forward for the Mac OS:
1) there will be things that don't work all that perfectly until vX.X.2. So be patient.
2) older hardware may perceive the up rev as a down rev, at least as far as performance goes. That's the way it always works. If your Mac is more than a year and a half old, once the bugs are worked out of Lion, you may not benefit as much as those with newer hardware, and there may be some compromises from the older OS versions that you won't be completely happy with.
My then-new 2006 Core 2 Duo Mac Mini booted in 15 seconds until I installed Leopard, for exactly that reason (that hardware was tuned for that software OS). Now it takes a minute and a half. Is that Leopard's fault? Hardly. That software OS no longer is tuned for that hardware. Stuff changes. The further out of sync your hardware becomes with newer OS releases, the less it will really shine on that older hardware.
But Apple is only going to tout the positive. It makes no business sense to remind everyone that older hardware will have issues with newer software, even though that is the cold reality. They try to tell us each time that performance will be better. I usually is, but what they fail to tell us is that performance will be better
on new hardware, but possibly not even as good as it used to be when used on older hardware.
Apple has everything first but also moves away from everything first. It's their version of planned obsolescence. Apple brought us the plastic-cased floppy years before anyone else, and later they ripped it away from us years before anyone else, although probably just at the right time. Time marches on and Apple drives that issue, taking no prisoners and leaving anyone who won't go along in the dust. Lion is just another forward step; toward the future, but leaving the past where it belongs, in the past. And leaving us no other real option than to try to keep up.
The window where hardware and software OS are in tune with each other is short. The pattern has always been that hardware and software progress together, and Apple tunes the latest software to the latest hardware at the sake of and even to the detriment of older hardware. So buy a new Mac when a significant new OS releases on brand-new significantly-advanced hardware. A perfect example would be an i5 or i7 box shipping with Lion. Up rev it (major versions) twice. Up rev it a third time at your own risk, because at that point you are trying to put lipstick on a pig. But normally, that will be 3-5 years down the road and you will want new hardware anyway.
I bought a 12" PB top-of-line laptop in 2003 the day it came out, and it was relevant until Snow Leopard, about the time the Mac App store launched. It still works just fine running Leopard, BTW. But the only mistake I made was buying the very top of the line, which made it future proof actually a bit too long. But I can't complain about 8 years out of a laptop I lugged to work every day. Three years is about average.
I did not make that mistake (too much future-proofing) with the new Air, buying only the i5. That way it will hopefully become obsolete only when the software also becomes obsolete and the then new software won't work with it all that well. And then, well, time for new hardware/software again.
That's the reality of how the Apple culture works. To take best advantage you have to upgrade hardware at the right time; you have to be in tune with the cycles. Those who don't do this, or unfortunately can't afford to do this, get left behind to a certain extent.
Apple does not care, and does not feel our pain, they became the highest-valued company in the world by forcing that cycle to work, and consequently selling tons of top-shelf gear that becomes obsolete every three years because of them forcing that cycle. We either go along, and pay the price, or suffer a comparatively degraded experience. It still beats any other computer experience all to hell.
